Sugar may, under some circumstances for some people, increase heart rate. A search of the Internet reveals mixed assertions as to the immediate effects of sugar on heart rate. But research--such as that of Kennedy and Scholey summarized at Springer Link--and an understanding of the physiology involved in the metabolism of sugar suggest sugar can affect heart rate in the short, medium and long term via varied mechanisms.
Fuel for Thought
Your body requires fuel in order to operate. The food you eat is your fuel. It's digested and converted into glucose, a form of blood sugar, which is then used by cells for the energy required for everything your body does--from thinking to breathing to running. Some foods, referred to as high glycemic index (GI) foods, are converted into glucose more quickly than other foods. Sugar is a high GI food. When you consume simple processed sugar, it can be converted into blood glucose within minutes. This short time required to convert sugar into blood glucose is one reason people turn to sweets for a quick pick-me-up. Complex carbohydrates such as vegetables and fruit or proteins including nuts, fish and meat take much longer to be converted into cellular fuel.
When blood glucose is high, the pancreas releases insulin, which then helps to transport glucose into muscle or liver cells. There, it's used for energy. If there's more glucose present than needed, insulin helps the glucose to be stored in adipose tissues as fat for potential future energy needs. One immediate effect of the breakdown and conversion of glucose into cellular energy is an increased metabolism, which can manifest itself in the form of increased heart rate, high blood pressure or some other form of arousal such as heightened mental alertness. A study by Kennedy and Scholey described at Springer Link found that study participants had greater increases in heart rate and performed better when given mental tasks following administration of glucose than control subjects who did the same tasks without glucose. People have individualized responses to heightened metabolism, so sugar may not always cause a noticeable change in heart rate for all individuals. In Kennedy and Scholey's study, subjects who had lower baseline heart rates had the greatest performance enhancements following glucose administration.
Once insulin has eliminated glucose from the blood, there's a condition of lowered blood glucose. People with diabetes or with other metabolic conditions such as reactive hypoglycemia or post-prandial reactive hyperinsulinemia can experience a sudden crash in blood sugars because their pancreas overreacts to the presence of blood glucose and releases too much insulin. The pancreatic reaction triggers a cavalcade of hormone responses, including the release of stress hormones such as epinephrine by the pituitary gland. These stress hormones stimulate the sympathetic nervous system and cause physiological arousal that can include--among other responses--heightened heart rate, increased blood pressure, hyperactivity, anxiety and irritability. For example, a study by Langseth and Dowd described at ADD ADHD Advances found that close to three-fourths of children diagnosed with ADHD who showed hyperactivity after sugar consumption had reactive hypoglycemia. For those who suffer from metabolic dysfunction, conditions of low blood sugar, which occur several hours after consuming sugar, can cause an increase in heart rate.
Sugar accounts for 25 percent of Americans' caloric intake. The weighty truth is that our obsession with sugar, along with a growing aversion to exercise, has rendered us obese. Remember, insulin converts blood glucose it can't use for immediate energy into fat. The extra girth we carry burdens our heart and contributes to escalating cardiac disease--including hypertension, high blood pressure and elevated heart rate.
You can benefit from the heightened mental and physical energy that food provides without stressing your metabolic system or posing risks to your cardiovascular system. Minimize consumption of simple sugars and starches, and instead consume complex carbohydrates such as fruits, vegetables and whole-grain foods. These foods take longer to release sugars into your blood and provide your brain and body with a steady source of glucose.